Method of treating paper containers



, Patented May 16, 1939 UNITED STATES PATENT OFFICE No Drawing.Application October 8, 1937, Serial No. 167,979

v Claims.

This invention relates to a method of treating paper containers.

Paper containers for liquids and semi-liquids such, for example, as milkand other dairy prod- 5 ucts, are replacing glass to a considerableextent.

Paper containers for milk, for example, have various advantages overglass bottles. Perhaps the principal ones are that paper containers,being used once only, avoid all the difliculties and complications ofreturns of empties, loss by breakage and the necessity of maintainingwashing equipment at the dairy.

A paper container for liquids such as milk must be specially treated torender the container as nearly moisture-proof as possible. The commonmethod is to subject the container to a bath of molten paraffin or othersuitable material by dipping or spraying.

While the paper container should have an inner and outer surface coatingof paraffin (that material being cited herein by way of example),coating alone is not enough. To obtain a properly moisture-proofedarticle, the paper stock shouldbe thoroughly impregnated with the paraifln.

I have found that with the paraiiiningtreatment as ordinarily practiced,the results are somewhat unsatisfactory because full impregnation of thepaper stock is not attained, at least without such an extended durationof treatment, preheating and the like, as to render the processcommercially impractical. That is, the problem is not only to obtainproper impregnation but also -to obtain it in such a way that it can beput into commercial use. The ordinary glass milk bottle is used over andover. In addition, the dairy has a sufficient supply on hand for itsdaily requirements. Paper containers, on the other hand, are used onceand thrown away. It is apparent that if paper containers are to competecommercially with glass bottles, they must be produced at low cost. Butany steps that slow up production raise'the cost. Moreover, it is ausual practice for dairies to make their paper containers at the dairyas needed. It follows that any treating process, to be commerciallypractical, must make it possible for the containers to be produced atsuch speed as will enable the dairy to obtain its daily requirementswithout excess equipment.

It is an object of the present invention to provide a method of treatingpaper containers such that the containers are properly moisture-proofedin that they have a surface coating of and are thoroughly impregnatedwith the moisture-proofing material; and such that the treatmentreferred to can be effected in a rapid and otherwise commerciallypractical manner.

With these and other objects in view, the invention consists in themethod and method steps 6 which will first be described and then moreparticularly pointed out.

, I have discovered that a thorough impregnation may be obtained in arelatively brief period of time if the paraffin bath is at a temperature10 of at least 212 F., i. e., at least as high as the boiling point ofwater. It is my belief that the failure to obtain proper impregnationunder previously known treatment methods results from the fact that airand moisture become entrapped in the fibers of the paper stock andprevent, in whole or in part, entrance of the molten paraflin. It is myfurther belief that treatment at 212 F. or over causes an expansion ofany air and a dissipation of any moisture that may be present in thestock, thus permitting a thorough impregnation of the stock by theparaflin.

While treatment at the temperatures referred to results in satisfactoryimpregnation, I have found in the course of my experiments that suchtreatment was by nomeans the complete so1ution of the problem and, infact, created new problems. For example, while paraffin at 212 F. orhigher will impregnate the paper stock, it will not adhere to thesurface in the form of a coating, at least not to the extent necessaryfor a satisfactory product. Further, treatment at such temperatures isapt to char the paper. In this connection, the word char is used todenote any damage to or discoloration of the paper due to heat.

In other words, if the containers are treated at a temperature highenough to obtain proper impregnation, they lack proper surface coatingand are apt to be charred. On the other hand, if the temperature isreduced sufficiently to avoid charring and obtain a suitable surfacecoating, satisfactory impregnation is not obtained.

The matter of charring is of considerable importance, particularly inthe case of containers for'milk. Many containers are moisture-proofed ina partially completed condition. That is, after filling some additionalfolding, creasing or similar steps are necessary to complete and closethe ultimate container. If thecharring is of such character as to damagethe fibers of the paper stock, the paper is apt to become brittle andlifeless so'that subsequent folding, creasing or other fabricatingoperations cannot be properly carried out, at least commercially. If thecharring is merely a discoloration of the paper, while there may be noactual damage, the container is useless commercially because the publicwillnot buy milk and the like in containers that have any imperfections,even in appearance.

According to the invention in its entirety, I subject the containers toa bath of paraflin or other suitable moisture-proofing material at atemperature at least as high as the boiling point of water. I maintainthe container in such bath for a period of time sufiicient to obtainproper impregnation but insuiiicient to cause any substantial charringof the paper stock. I then remove the container from the aforesaid bathand subject it to a cooling bath before the heat stored up in the papercan cause any substantial charring.

In accordance with the invention in its entirety, this cooling bath isalso of a moistureproofing material, such, for example, as paraffin. Itstemperature is substantially below 212 F. Thus, the second bath performsa double function., It is a cooling bath and a coating bath. Theparaflin in this bath is relatively cool enough to cool oh the paperbefore charring can occur. It is also cool enough to result in a surfacecoating on the container.

The temperature of the impregnating bath and the time of treatmenttherein may vary within a considerable range. While time and temperatureare generally reciprocal, one may be varied more or less without varyingthe other. For paper stock such as isordinarily used in the manufactureof paper containers, I have found a bath temperature of around 245 F.and a treatment period of a few seconds, i. e., less than a minute,gives satisfactory results. In fact, at this temperature, thoroughimpregnation can be obtained almost as rapidly as it is possible toinsert and remove the containers, at leaston a commercial scale. Itfollows that there is nothing particular to be gained by increasing thetemperature or decreasing the time.

While the interval between the impregnating bath and the coating bathmay vary, the paper stock is apt to char, at least as to surfacediscoloration, if allowed to stand in the air any considerable time. Ihave found that the best results are obtained if the containers, afterremoval from the impregnating bath, are immediately subjected to thecooling and coating bath, that is, as quickly as it is practicallypossible to effect the transfer.

The temperature of the cooling and coating bath and the time (itreatment therein may also vary within a considerable range. Thetemperature must, of course, be far enough below 212 F. for the bath toperform its cooling and coating functions and should be high enough tomaintain the bath material in proper liquid condition.

With molten paraffin as the second bath material, I have found thatcharring may be prevented and the containers properly coated in a fewseconds, i. e., less than a minute, with a paraffin temperature of aboutF.

With the method herein described, paper containers may be produced thatare properly moisture-proofed in that they have both surface coating andthorough impregnation. But what is perhaps of equal or greaterimportance is that these ends are attained in a relatively brief timeperiod. Not only does reduction of time of manufacture reduce the cost,but in many dairies, rapid production is essential to dairy operation.Forvv various reasons it is desirable, and in some jurisdictionsobligatory, to paraffin milk containers on the day of filling. In suchcases, a dairy having a volume running into tens of thousands of quartsmust be able to produce or treat its containers in the least possibletime. By making it possible to moisture-proof containers in a matter ofseconds, the method here described contributes largely toward theattainment of that end. Moreover, the cooling bath cuts down the coolingperiod prior to handling and other subsequent operations. I

Thorough impregnation not only makes possible a properlymoisture-proofed container but also has another advantage. The paperstock ordinarily used in making containers is normally opaque. The morethe stock becomes impregnatedwith parafiin or the like; the less opaqueand the more translucent it becomes. 'With good grade stock and thethorough impregnation made possible by the present invention, the stockmay be made so translucent as to be almost transparent.

' This is of particular importance in packaging milk as the containerstock becomes sufficiently translucent to make the cream line clearlyvisible.

It is to be understood that other materials than paraflin may be used;that container is intended to include partially or roughly finishedcontainers, container blanks, etc.; and that the bath may be byspraying, dipping or in any other suitable manner.

This application is a continuation, at least in part, from applicationSerial No. 679,210 filed July 6, 1933. r

What is claimed is:

1. The method of paraflin or similar paper containers which comprisessubjecting the containers to a bath of moisture-proofing material at atemperature at least as high as the boiling point of water, whereby thepaper of the containers is impregnated with said material, removing thecontainers from such bath after a time interval insufficient to causecharring of the containers and, substantially immediately after suchremoval, subjecting the containers to a bath of paraffin or similarmaterial at a temperature substantially below the boiling point ofwater, whereby said containers are cooled by and become coated with saidmaterial.

2. The method of parafiin or similar paper containers which comprisessubjecting the con- I tainers to a bath of moisture-proofing material ata temperature at least as high as the boiling point of water and for arelatively brief interval of time, whereby the paper becomes impregnatedwith said material, and substantially immediately subjecting thecontainers to a bath of parafiin or similar material at a a temperaturesubstantially below the boiling point of water, whereby said containersare cooled by and become coated with said material.

3. The method of moisture-proofing paper containers which comprisessubjecting the containers to an impregnating bath of liquid paraflin or.

similar material at a temperature at least as high as the boiling pointof water and, before there is any substantial charring of the paper,subjecting said containers to a cooling and coating bath of paraflin orsimilar material.

4. The method of producing moisture-proof paper containers whichcomprises first submitting the containers to an impregnating bath ofmolten paraffin having a temperature of 212 F. or above, removing thecontainers after a time interval insufficient to cause any substantialcharring of the paper and, substantially immediately after such removal,subjecting the containers to a coating and cooling bath of moltenparafiin havinga temperature substantiallyless than 212 F.

5. The method of moisture-proofing paper containers which comprisessubjecting the containers to a bath of parafiin or similar material at atemperature at least as high as the boiling point of water and for atime interval insuificient to cause any substantial charring o! thepaper, and then subjecting the containers to a coating bath of paraflinor similar material at a substantially lower temperature, said coatingbath being applied substantially immediately after the termination ofsaid time interval, whereby the coating bath also acts as a cooling.bath to prevent any substantial charring' of the containers.

- ROLAND K. REED.

